It is known to provide lamps with a cover panel to protect the reflector and the light source from soiling or damage. Such cover panels are formed in a flat or tray-like manner. Since stray light escapes from the cover panels, it is advantageous to use a flat cover panel in cases where it is intended to avoid the emission of a component of the light into the region to the rear of the lamp as well as possible, in order for example to avoid facades from being illuminated. In addition, in certain countries there are regulations and standards that prohibit light from being radiated into the sky and can only be conformed to by flat cover panels. Tray-like coverings are then disadvantageous, since stray light is diffused into the region to the rear of the lamp from the parts of the tray-like covering that project from the light exit opening of the lamp.
On the other hand, flat cover panels have the disadvantage that rays from the light source impinging on the light exit plane of the lamp at a shallow angle are reflected back by the cover panel more intensely into the reflector and into the lamp and cannot exit.